For many years it has been recognized that a windowshade made of translucent or transparent material could be provided with a vapor-deposited layer of aluminum, the aluminum layer optionally being protected from mechanical abrasion by a coating of varnish or the like; see U.S. Pat. No. 2,774,421. A distinct improvement over this early shade is shown in U.S. Pat. No. 3,290,203, where a polymeric barrier layer is applied over the vapor-deposited aluminum and a water-activatable adhesive thereafter employed to bond the sheet material directly to a windowpane. U.S. Pat. No. 3,681,179 shows the use of a different type of water-activated adhesive, viz., a normally tacky and pressure-sensitive adhesive temporarily detackified by a thin layer of water-soluble material. Alternatively, the detackifying layer may be omitted and a removable liner substituted therefor at some additional cost and inconvenience. Reusable energy control products have been made by employing plasticized vinyl resins as the adhesive, providing a "cling" adhesion to windowpanes; see U.S. Pat. No. 4,095,013.
Other modifications of the energy control sheet material concept are shown in U.S. patent application Ser. No. 56,905, filed July 12, 1979 (now U.S. Pat. No. 4,276,910) and assigned to the assignee of the present invention; the energy control sheet material there described is directed to maintaining long wave infrared radiation, originating from inside a room, within the room, thereby enhancing its usefulness in cold climates and winter applications. The barrier layer may be applied from solution or extruded, but is typically a pre-formed self-supporting polymeric film adhered to the exposed aluminum surface with a thin layer of polymeric adhesive.
While all of the products just discussed have attained an extremely significant position in the marketplace, they have suffered from common problems, for which no one heretofore has provided a satisfactory solution. To some degree in any installation, and particularly where conditions are both sunny and humid, there has been a tendency for the aluminum layer to corrode to a transparent oxide form. Such corrosion may take place either locally, generating "pin holes" which gradually increase in size, or generally, causing a gradual "fading" which results in an overall loss of effectiveness of the energy control sheet material. This problem has been exacerbated by the fact that it is common to include ultraviolet light absorbers in the barrier layer in order to prevent such light from entering the interior of a room, where it has a tendency to bleach and degrade any fabrics which it strikes. For reasons which have never been adequately explained, the benzophenone ultraviolet light absorbers, which are most effective in excluding UV radiation from a room interior, tend to increase the rate at which the aluminium layer corrodes.